As is well known in the art, most small form factor disk drives utilize a ramp load/unload process wherein disk drive heads are loaded onto a disk (i.e., placed in position to read/write data from/to the disk) by causing an arm holding the heads to rotate so that it moves down along a ramp. Further, as is also well known in the art, when data access from/to the disk is complete, the disk drive heads may be unloaded from the disk by causing the arm to rotate so that it moves up along the ramp.
In order to ensure long-term disk drive reliability, the above-described ramp load/unload process should be controlled so that no damage to the disk and disk drive heads occurs. Generally, this involves using a servo control system that attempts to maintain the load and unload velocity of the disk drive heads on an optimized trajectory. As is known, this entails, among other things, measuring disk drive head velocity during the load/unload process.
As is well known, movement of disk drive heads is caused by applying current to a voice coil magnet (“VCM”) which causes an arm holding the disk drive heads to rotate. Prior art methods to measure the resulting disk drive head velocity typically entail using an analog-to-digital converter to measure a back-EMF voltage generated in the VCM. As is well known, the VCM back-EMF is proportional to an angular velocity of the VCM, and hence, provides a measure of disk drive head velocity. Such prior art methods are problematic because they require circuitry that: (a) is frequently complex, and (b) requires additional space on printed circuit boards. As a result, such prior art methods result in increased disk drive cost.
In light of the above, there is a need to overcome one or more of the above-identified problems.